Microelectromechanical devices (also called micromechanical devices or micromachines) are small (micron scale) machines that promise to miniaturize instrumentation in the same way microelectronics have miniaturized electronic circuits. Microelectromechanical (MEM) devices have configurations analogous to conventional macroscale machinery, such as cantilevers, motors, and gear trains.
The present invention is related to MEM cantilever devices, and analogous resonating structures. It is known to use the deflection of a MEM cantilever device to measure physical phenomena, such as small mechanical pressure variations associated with sound. A patent application entitled "Cantilever Pressure Transducer", Ser. No. 08/072,294, filed Jun. 10, 1994 , now abandoned, and assigned to the assignee of the present invention, discloses one such device.
It would be highly desirable to provide a MEM cantilever device with the capability of measuring different physical phenomena. Such a device would enable the exploitation of other benefits of MEM devices, such as their compactness and low power consumption.
If the structure of a MEM cantilever device was suitably improved, it could be used, for example, to reliably measure an electric field associated with a power line. This would potentially provide a compact and low-power power line sensor.
Electric utilities are interested in monitoring power parameters, such as current and voltage, along the length of powerlines. This information is useful in locating powerlines that have failed, are failing, or have some other undesirable attribute, such as arcing activity, voltage sag, momentary outage, improper loading, or poor "power quality" as evidenced by the presence of harmonics of the power line frequency.
Shortcomings associated with existing power line sensors make it difficult to provide comprehensive power line monitoring. Existing power line sensors are relatively expensive because they require insulation of the current or voltage transducers for the full electric potential of the power line. The insulation is expensive and bulky. In addition, existing sensors typically require a connection to ground, thereby necessitating a physical electrical connection from the power line to the ground. Consequently, existing power line sensors are inherently expensive, bulky, and expensive to install. It would be highly desirable to provide a power line sensor which could operate without the insulation and ground connection associated with prior art power line sensors. Such a device would be compact and relatively simple to install. Preferably, such a device would be inexpensive and have low maintenance requirements.
Improvements in power sensing are also desirable for watt and watt-hour meters at customer locations. It would be highly desirable to provide a compact, reliable, inexpensive solid-state power meter.